Polyamides represented by polyamide 6 and polyamide 66 (hereinafter, sometimes referred to as “PA6” and “PA66”, respectively) and the like have excellent molding processability, mechanical properties, or chemical resistance. Therefore, polyamides are widely used as a material for various parts, such as for automobiles, electric and electronic parts, industrial materials, and daily and household articles.
In the automotive industry, as an environmental measure, there is a need to lighten the weight of the automobile body by using a metal substitute in order to reduce exhaust gases. To respond to this need, polyamides are being increasingly used for exterior materials, interior materials and the like. Further, the level of the properties required for polyamide materials, such as heat resistance, strength, and appearance, is dramatically increasing. However, the temperature in the engine room is also tending to increase, so that the need to increase the heat resistance of polyamide materials is growing stronger.
Further, in the electric and electronics industry, such as household appliances, there is a need for increased heat resistance for polyamide materials which are capable of withstanding the increased melting point of the solder required for lead-free solder for using surface mounting technology (SMT).
PA6 and PA66 polyamides are unable to satisfy these requirements in terms of heat resistance, since their melting point is low.
To resolve the above-described problems with conventional polyamides such as PA6 and PA66, a high-melting-point polyamide has been proposed. Specifically, a polyamide formed from terephthalic acid and hexamethylenediamine (hereinafter, sometimes referred to as “PA6T”) has been proposed.
However, PA6T is a high-melting-point polyamide having a melting point of about 370° C. Therefore, even if a molded product is obtained by melt kneading, pyrolysis of the polyamide is severe, which makes it difficult to obtain a molded product having sufficient properties.
To resolve the above-described problem with PA6T, a high-melting-point semi-aromatic polyamide (hereinafter, sometimes referred to as “6T-based copolyamide”) and the like comprising terephthalic acid and a hexamethylenediamine as main components has been proposed. This high-melting-point semi-aromatic polyamide has a melting point lowered to about 220 to 340° C. by copolymerizing an aliphatic polyamide, such as PA6 and PA66, and the amorphous aromatic polyamide formed from hexamethylenediamine and isophthalic acid (hereinafter, sometimes referred to as “PA6I) and the like with PA6T.
As a 6T-based copolyamide, Patent Document 1 describes an aromatic polyamide (hereinafter, sometimes referred to as “PA6T/2MPDT) which is formed from an aromatic dicarboxylic acid and an aliphatic diamine, in which the aliphatic diamine is a mixture of hexamethylenediamine and 2-methylpentamethylenediamine.
Further, in contrast to an semi-aromatic polyamide formed from an aromatic dicarboxylic acid and an aliphatic diamine, a high-melting-point aliphatic polyamide (hereinafter, sometimes referred to as “PA46”) formed from adipic acid and tetramethylenediamine, and an alicyclic polyamide formed from an alicyclic dicarboxylic acid and an aliphatic diamine, and the like have been proposed.
Patent Documents 2 and 3 describe a semi-alicyclic polyamide (hereinafter, sometimes referred to as “PA6C copolyamide”) which is formed from an alicyclic polyamide (hereinafter, sometimes referred to as “PA6C”) formed from 1,4-cyclohexanedicarboxylic acid and hexamethylenediamine, and another polyamide.
Patent Document 2 describes that electric and electronic parts formed from a semi-alicyclic polyamide blended with 1 to 40% of 1,4-cyclohexanedicarboxylic acid as a dicarboxylic acid unit have improved solder heat resistance. Patent Document 3 describes that for automobile components, fluidity, toughness and the like are excellent.
In addition, Patent Document 4 describes that a polyamide formed from a dicarboxylic acid unit comprising 1,4-cyclohexanedicarboxylic acid and a diamine unit comprising 2-methyl-1,8-octanediamine has excellent light fastness, toughness, moldability, low weight, heat resistance and the like. Moreover, as a production method for such a polyamide, Patent Document 4 describes that a polyamide having a melting point of 311° C. is produced by reacting 1,4-cyclohexanedicarboxylic acid and 1,9-nonanediamine at 230° C. or less to produce a prepolymer, which is then subjected to solid phase polymerization at 230° C.
Further, Patent Document 5 describes that a polyamide using 1,4-cyclohexanedicarboxylic acid having a trans/cis ratio of from 50/50 to 97/3 as a raw material has excellent heat resistance, low water absorbance, and light fastness.    Patent Document 1: National Publication of International Patent Application No. 1994(Hei 6)-503590    Patent Document 2: National Publication of International Patent Application No. 1999(Hei 11)-512476    Patent Document 3: National Publication of International Patent Application No. 2001-514695    Patent Document 4: Japanese Patent Laid-Open No. 9-12868    Patent Document 5: WO 2002/048239 pamphlet